Well known in the art is a so-called twin roll continuous casting apparatus in which a pair of internally cooled rolls having respectively horizontal axes and rotating in opposite direction to each other are disposed parallel to each other with an appropriate gap therebetween, a pool of molten metal is formed on the circumferential surfaces (the upper halves cylindrical surfaces in the axial directions) of the rolls above the gap and the molten metal is continuously cast into a metal strip through the gap while being cooled by the circumferential surfaces of the rotating rolls. There has also been proposed such a twin roll continuous apparatus applied to a case of continuous casting of steel to produce a steel strip directly from molten steel.
When a metal strip is continuously cast through a gap between a pair of rolls, it is necessary to form a pool of molten metal on the circumferential surfaces of the pair of rolls above the gap therebetween and to maintain a level of the molten metal in the pool substantially constant by continuously pouring the molten metal into the pool. In order to form the pool of molten metal, there are required a pair of dams having their surfaces perpendicular to the roll axes which prevent an overflow of molten metal along the roll axes on the circumferential surfaces of the rolls. These dams also serve usually to regulate the width of the cast strip and are referred to herein as "side dams". In addition to the side dams disposed at the left and right sides of the rolls, a pair of front and rear dams (referred to herein as "longitudinal dams") having their surfaces along the roll axes may be erected orthogonally to the side dams on the circumferential surfaces of the rolls so as to form a box-like pool for molten metal with the side dams and the longitudinal dams. The box-like pool serves to prevent waves of molten metal in the pool from directly hitting the surfaces of the rolls, thereby preventing formation of wrinkles (called "molten metal wrinkles") on the surfaces of the cast strip.
If the longitudinal dams are erected on the surfaces of the rolls so as to intercept the molten metal in the pool by inside surfaces of the dams, as shown in FIG. 4, the molten metal stagnates at those corners of the pool, which are formed by the inside walls of the longitudinal dams and the surfaces of the rolls, where it is liable to be solidified forming so-called triple point shells on lower edges of the longitudinal dams, since it is cooled by both the longitudinal dams and rolls. When the triple point shells grow to a certain size, they drop from the longitudinal dams and are incorporated in surfaces of the strip being cast, causing defects of the product.